Scintillation camera

ABSTRACT

In a gamma ray imaging camera having a scintillation crystal and a plurality of phototubes, two channels are provided for receiving and processing radiation of two different energy levels arising from injection into a patient of two different radioisotopes. Signals in the two energy ranges may both be recorded for future analysis or may be displayed side-by-side on an oscilloscope. Regardless of whether one or two isotopes are used, information describing the locations of scintillation in the crystal may be digitized, recorded, and played back for visual display at a later time. Alternatively, the location information may be displayed immediately. Calibration means are also provided for presenting the output of each phototube individually on an oscilloscope so that the apparatus may be adjusted to correct for variations inherent in phototubes.

United States Patent Martone et al.

Sept. 9, 1975 Assignee:

Filed:

SCINTILLATION CAMERA Inventors: Ronald J. Martone, Cheshire; Peter G.Mueller, Guilford, both of Conn.; Robert Hindel, Weisbaden, GermanyPicker Corporation, Cleveland,

Ohio

Sept. 1 1, 1972 Appl. No.: 287,623

Related U.S. Application Data Continuation of Ser. No. 198,520, Nov. 15,1971,

abandoned, which is a continuation of Ser. No. 837,072, June 27, 1969,abandoned.

[52] U.S. Cl 250/369; 250/366 [51] Int. Cl. G0lt 1/20 [58] Field ofSearch 250/252, 366, 367, 369

[56] References Cited UNITED STATES PATENTS 3,011,057 11/1961 Anger250/366 3,308,438 3/1967 Spergel et a1. 340/1725 3,327,116 6/1967Loveday 1 250/366 3,509,341 4/1970 Hindel et al.. 250/366 3 634,6881/1972 Di Rocco 250/366 PHA I l 1 7'0 66F I Primary Examiner-Archie R.Borchelt Attorney, Agent, or Firm-Watts, Hoffmann, Fisher & Heinke [5 7ABSTRACT In a gamma ray imaging camera having a scintillation crystaland a plurality of phototubes, two channels are provided for receivingand processing radiation of two different energy levels arising frominjection into a patient of two different radioisotopes. Signals in thetwo energy ranges may both be recorded for future analysis or may bedisplayed side-by-side on an oscilloscope.

Regardless of whether one or two isotopes are used, informationdescribing the locations of scintillation in the crystal may bedigitized, recorded, and played back for visual display at a later time.Alternatively, the location information may be displayed immediately.

Calibration means are also provided for presenting the output of eachphototube individually on an oscilloscope so that the apparatus may beadjusted to correct for variations inherent in phototubes.

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/N FROM P/-/9 INVENTOI25 QOMALD J. MAeTa/ve PETE/2 a. MUELLER ATTNESCINTILLATION CAMERA This is a continuation, of application Ser. No.198,520, filed Nov. 15, 1971, which application is a continuation ofprior parent application Ser. No. 837,072, filed June 27, 1969 and bothare now abandoned.

CROSS-REFERENCES TO RELATED PATENTS AND APPLICATIONS 1. RE 26,014 issuedMay 3, 1966 to J. B. Stickney et al, reissue of US. l at. No. 3,070,695dated Dec. 25, 1962 entitled Scintillation Scanner."

2. Copending application Ser. No. 739,793 filed June 25, 1968 by PeterG. Mueller entitled Pulse Height Analyser.

3. Copending application Ser. No. 739,889 filed June 25, 1968 by Roberti-Iindel entitled Scintillation Detector Indicating System.

4. Copending application Ser. No. 834,346 filed June 18, 1969 by RonaldJ. Martone et al for Scintillation Camera System.

5. Copending application Ser. No. 834,478 filed June 18, 1969 by RonaldJ. Martone et al for Scintillation Camera System.

6. Copending application Ser. No. 836,915 filed June 26, 1969 by RonaldJ. Martone et al for Digital Recording-Playback Technique.

BACKGROUND OF THE INVENTION 1. Field of the Invention.

This invention pertains to gamma imaging devices and more particularlyto that class of device known as scintillation cameras.

In the diagnosis of certain illnesses, radioactive isotopes areadministered to patients. Many administered isotopes have thecharacteristic of concentrating in certain types of tissue and eithernot concentrating in or concentrating to a lesser degree in other typesof tissue. For example, iodine 131 collects in thyroid glands. A graphicimage produced to show the spatial distribution and concentration ofthis isotope in the thyroid gland provides an image of the thyroid glanditself. This image is useful in diagnosing a patients physicalcondition.

2. Summary of the Prior Art.

Generally speaking, the devices used for producing graphic images of thedistribution of an isotope in a subject are known as scanners andcameras. With a scanner, a scintillation probe is moved rectilinearlyalong a plurality of spaced parallel paths. The energy detected isutilized to make either a photographic or a dot image reflecting thespatial distribution and concentration of the isotope in the subject. Aclinically successful scanner is described in greater detail in theabove-referenced US. Pat. RE 26,014 to J. B. Stickney et al.

The devices known as cameras remain stationary with respect to thepatient as the graphic image of the spatial distribution of an isotopeis developed. Many cameras use an instrument where a relatively largedisc-like scintillation crystal is positioned to be bombarded by gammaradiation emitted by a patient. With most cameras, a collimater isinterposed between the patient and the crystal. The crystal converts thegamma ray energy impinging on it to light energy. This light energy isin the form of light flashes or scintillations. In one class of camera,a thalium-activated sodium iodide crystal is typically utilized. Sincesodium iodide is highly hygroscopic, it is encapsulated with anhermetically sealed envelope. A plurality of phototubes are positionednear the crystal. When a phototube detects a scintillation, anelectrical signal is emitted by the phototube. The electrical signalemitted by the phototube is of an intensity which is proportional bothto the intensity of the light flash and its distance from the phototube.

Signals emitted simultaneously by the camera phototubes are amplifiedand then conducted to electronic circuitry. The preferred circuitry isdescribed in greater detail in the referenced applications. Thiscircuitry includes a pulse-height analyzer to determine whether or notthe signals in question reflect the occurrence of a so-called photopeakevent. Summing and ratio circuits,

are included which result in the signal being sent to an oscilloscope tocause a light signal to be emitted by the oscilloscope. The objective isthat the oscilloscope signals be displaced relatively each at a locationcorresponding to the location of a corresponding scintillation in thecrystal.

It is a general object of the present invention to provide a moreversatile camera than has heretofore been available.

It is a more specific object to provide such an instrument that iscapable of resolving radiation emanating from either one or both of tworadioactive isotopes and displaying a graphic image of the spatialdistribution of radiation from either isotope or of both isotopes.

It is a further object to provide an instrument that incorporatesrecording and playback apparatus, and that incorporates an improvedtechnique for calibrating the phototube section of the instrument.

SUMMARY OF THE INVENTION Output signals from the nineteenphotomultipliers comprising the detector assembly are provided todecoding matrices whose output signals represent the location of thescintillation in terms of X+, X-, Y+ and Y location signals. A Z signalis also provided that represents the sum of the outputs of all of thephototubes. Means are also provided in connection with the decodingmatrices for selecting any one of the phototube outputs for calibrationpurposes.

The decoded position signals are then supplied to two analog computers,which are adjusted to accept signals resulting from scintillationshaving two different energy levels. Thus, one channel may be adjusted toaccept signals resulting from radiation by one isotope, and the otherchannel adjusted to accept radiation from a second isotope. The four Xand Y signals from either channel are then combined and converted into asingle X signal and a single Y signal.

In one mode of operation, the X and Y position indicating signals areconverted to digital signals, which may be recorded on a magnetic mediumfor future ref erence. Those digital signals are also reconverted toanalog signals for display purposes. The latter analog signals areprovided to a rotator, which mixes them in sine/cosine weights to rotatethe image being displayed in accordance with the viewers preferences.The signals are also supplied to a data processor where additionaloperations may be performedon them.

In another mode of operation, the X and Y signals are not converted intodigital signals, but rather are supplied directly to the rotator andthen displayed. In

that mode of operation, the signals are not recorded and hence are lostso far as future reference is concerned.

In a third mode of operation, signals are sent from any selected one ofthe various phototubes directly to the data processor. The dataprocessor operates on those signals and displays the gamma ray spectrumof pulses from the particular detector selected. This mode of operationis used for calibration purposes.

Circuitry is provided in conjunction with the display Oscilloscopes topermit the display of information from both isotope channels on theoscilloscope in side-byside relationship. Alternatively, informationfrom only one of the channels can be presented. The technique ofdisplaying information from both channels, however, has been found toprovide a valuable diagnostic tool.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational view of acamera and associated consoles utilizing the invention;

FIGS. 2(a) and 2( [7) are block diagrams of a camera system embodyingthe invention;

FIGS. 3(a) and 3(1)) are a combined circuit and block diagram ofattenuators and decoding matrices that provide input signals to theanalog computers;

FIG. 4 is a schematic diagram of an attenuator used in the diagram ofthe FIG. 2; and

FIG. 5 is a diagrammatic representation of the arrangement of phototubesin the detector head of the camera.

DESCRIPTION OF A PREFERRED EMBODIMENT It was mentioned in theintroduction that a camera embodying the present invention can operatein at least three modes. The first of these, which is designated thenormal mode, is the most commonly used and is the most complex so far asthe interrelationship of parts and signals are concerned. The secondmode, which is known as the fast analog" mode, does not utilize thedigitizing and recording portion of the apparatus, and hence is muchsimpler in its operation. A test" mode is utilized for calibrating theindividual phototubes comprising the detector assembly. A playback" modeinvolves playing back information recorded on a magnetic mediumand doesnot require the use of a great many of the components utilized in thenormal mode of operation. Therefore, the normal mode operation will bedescribed in detail and the other modes described considerably morebriefly.

In FIG. 1, the detector head is shown generally at 10. The head isadjustably mounted on a stand 1 1 for positioning adjacent a patient orother subject. Electrical signals from the head are conducted tocircuitry contained within the console shown generally at 12.

The signals, after processing by the circuitry, produce a graphic imageof the subject under investigation on a monitor oscilloscope 13. Aduplicate image is produced on a camera oscilloscope, not shown, whichis viewed and photographed by a camera 14.

The circuitry in the console 12 first produces analog signals in mannersto be morecompletely described hereinafter. Assuming the analog signalsrepresent photopeak events, they are digitized. The digital signals maybe fed to a computer for analysis and diagnosis.

The digital information is also fed to a builtin data processor 15. Thisprocessor utilizes the digital information to generate a variable-widthprofile histogram of counts versus horizontal distance or a histogram ofcounts versus time. Such histograms are displayed on a monitoroscilloscope l7.'The digital information is also fed to a tape recordingconsole shown generally at 19 for storage and subsequent utilization.The digital information is reconverted to analog form to produce theimages displayed on the monitor oscilloscope l3 and recorded by thecamera 14.

The detector head 10 is shown and described in detail in copendingapplication Ser. No. 833,552, filed,

as comprising a plurality of phototubes Pl P19. The

phototubes P1 P19 are arranged in an hexagonal array. Certain ones ofthe phototubes are utilized to determine the location of a scintillationin terms of X+, X-, Y+ and Y- coordinates. Also, the output signalsfrom'all of the phototubes Pl P19 are summed to pro vide a Z signal.This will become more apparent from the description of FIG. 2.

The signals from the 19 phototubes P1 P19 are respectively amplified in19 preamplifiers containedin a preamplifier assembly 20 located in thedetector head, and then attenuated to various degrees in an attenuatorassembly 22 located in the console 12. The attenuator assembly 22 willbe described in greater detail in connection with FIG. 3. However, itsprimary purpose is to provide for calibrating the various phototubeswhich may differ in their individual gain characteristics.

From the attenuator assembly 22, the 19 signals are supplied to adecoding assembly 24 comprising six matrices labeled 24a 24f. The outputsignals of the decoding matrices 24a, 1), c, d, e, are supplied as inputsignals to two analog computers 26A, 268 connected in parallel.

The matrix section 24fincludes a selector switch (not shown in FIG. 2),which permits the output of any one of the 19 phototubes in the detectorassembly 10 to be routed through a test switch 28 and provided on a lead30 to the data processor 15 for calibration purposes. This feature ofthe invention will be described in more detail hereinafter.

Inasmuch as the two analog computers 26A, 26B are identical inconstruction, only the computer 26A will be described in detail.

The input signals to the analog computers 26A, 26B from the decodingmatrices 24a e are respectively provided to five variable gainamplifiers 32a e. The gains of all five of the amplifiers 32a e areremotely controlled from the front panel of the apparatus to permitreceiving scintillations having different energy ranges. The amplifiers32 are fully illustrated and described in the referenced applicationSer. No. 836,915, filed June 26, 1969 by Ronald J. Martone et al.

Output signals from the amplifiers 32a e are respec tively provided topulse stretchers 34a e, and the output from the amplifier 32a is alsosupplied as an input to a pulse height analyzer 36. Each analogcomputer26 also contains a ratio detector circuit 38. The pulse heightanalyzer 36 is shown and described in the referenced patent applicationSer. No. 739,793, and the pulse stretchers 34 and the ratio detector 38are similarly described in the referenced patent application Ser. No.739,889. Reference is made to those two applications for a completedescription of the components 34, 36, 38 comprising each of the analogcomputers 26A, 26B.

Suffice it to say, that on a lead 40b is present a signal thataccurately represents the X+ position of a scintillation occurring inthe scintillator, on a lead 400 is a signal accurately representing theX- coordinate of such a signal, on a lead 40d is a similar signalrepresenting the Y+ coordinate, and on a lead 40a is a similar signalrepresenting the Y- coordinate. Similar signals are provided on thoseleads from the channel B analog computer 26B. Gating means (not shown)are provided to insure that signals are not received simultaneously fromboth channels A and B. More specifically, if signals are being receivedfrom channel A, channel B is effectively disabled. In other words, onlyone channel is in control.

A timing circuit 42 receives signals on a lead 44 from the ratiodetectors 38 in both channel A and channel B analog computers, and on alead 46 from both pulse height analyzers 36 in those channels. Inputpulses are also provided to the timing circuit 42 on a lead 48 from atransfer gate 50 and on a lead 52 from a one-shot multivibrator to belater described. The timing circuit also sends a signal directly to thatmultivibrator when in the fast analog mode of operation. The timingcircuit 42 waits for a signal on the lead 52 indicating the end of acycle and then gives a reset signal to each pulse height analyzer 36. Italso provides a clear signal for the transfer gate 50 on a lead 54. Thetiming circuit 42 also provides enabling signals to other portions ofthe analog-todigital conversion circuitry on a lead 56. These will bedescribed later in more detail.

The four output signals from the stretchers 34b e are provided to twodifferential amplifiers 58X, 58Y. The X+ and X signals on the leads 40b,400 are provided to the amplifier 58X, and the Y-land Y signals on theleads 40d, 406. are provided to the amplifier 58Y. Each of theseamplifiers 58X, 58Y combines its respective input signals and providessingle output signals respectively representing X and Y locationcoordinates. The X coordinates from the output of the amplifier 58X areprovided to a hcight-to-time converter 60X, and the Y coordinateinformation is provided from the Y differential amplifier 58Y to aheight-totime converter 60Y.

The X and Y coordinate information is also respectively provided onleads 62X, 62Y to an additional.

component of the circuitry not yet described.

The heightto-time converters 60X, 60Y are conven tional components thatproduce gating pulses of constant predetermined amplitudes, whoselengths are pro portional to the amplitudes of the input signals to theconverters. The output signals of the converter 60X, whose timedurations are proportional to the amplitudes of the input signals fromthe differential amplifier 58X, are provided to a gate 62X. Similarly,the output of the converter 60Y is provided to a gate 62Y. Second inputsto the gates 62X, 62Y are provided from an oscillator 64. The oscillatoris actuated by the gating signals from either of the converters 60X,60Y, and provides a train of pulses in which the number of pulses iscontrolled by the longest output pulse from either of the converters60X, 60Y. At the end of the signal from the converter 60X, the gate 62Xis closed, even though the output pulse from the converter 60Y may notyet have terminated. When the longer of the pulses from the converter60X, 60Y terminates, the oscillator 64 is shut off and both gates 62Xand 62Y are closed. The

7 result is that a train of output pulses is provided from the gate 62Xthat is proportional in number to the height of the output pulse of thedifferential amplifier 58X, and a train of pulses is provided from thegate 62Y that is proportional in number to the height of the outputpulse from the differential amplifier 58Y.

The construction and function of the converters 60X, 60Y, the oscillator64, and the gates 62X, 62Y are comparable to those described in anarticle by D. H. Wilkinson, entitled A Stable Ninety-Nine Channel PulseAmplitude Analyzer for Slow Counting, proceedings CambridgePhilosophical Society, Volume 46, Part III, pgs. 5085l8 (1950).

The output signals from the gates 62X, 62Y are respectively provided toscalers 66X, 66y. The scalers serve to store the numbers of pulses whichnumbers are proportional in amplitude to the X and Y output signals ofthe differential amplifiers 58X, 58Y, respectively. The scaler 66 alsocontains a section 66F that receives and stores flag signals from thepulse height analyzers 36 in the channel A and channel B analogcomputers 26A, 26B that indicate from which of the two channels thesignals being stored are received.

The digital signals stored in the X scaler 66X, the Y scaler 66Y and theflag portion 66F are transferrable through a gate 68 to a shift register70. The. gate 68 is opened in response to a signal from the transfergate 50. The transfer gate 50 provides that signal to open the gate 68when coincidence occurs between the clear signal received from thetiming circuit 42 on the lead 54 and the signal received on lead 73 froma ring counter 72.

The ring counter 72 is shown and described in detail in referencedapplication Ser. No. 836,915, filed June 26, 1969 In addition to thecircuitry shown in that application, the ring counter 72 is alsoconnected to the oscillator 64 by means of a lead 74. As set forth inthe referenced application Ser. No. 836,915, filed June 26, 1969, thering counter has 24 different intervals. These various intervals providetiming signals that control various components of the apparatus. Thering counter 72 sends a signal on a lead 73 to the transfer gate 50indicating when information should be transferred from the scaler 66 tothe shift register 70. It also sends a signal to a record amplifier 76that indicates when digital information should be recorded by a videorecorder 78. A similar signal is sent to the shift register that enablesit to transfer information to the recorder 78 through the recordamplifier 76. An additional signal issent to a gate 80 that in turncontrols a transfer gate 82 between the shift register 70 and a displayregister 84. It is pointed out that both the X and Y digitized signals,as well as the flag signal, are stored in the shift register 70 and aretransferred through the gate 82 to the display register 84.

The signal from the gate 80 that is sent to the gate 82 is also sentthrough a delay circuit 85 to a one-shot flipflop 86 along with thesignal from the timing circuit 42. The flip-flop 86 generates a signalthat is provided to an intensification control 88 and, at thetermination of that signal, also generates a signal that is returned tothe timing circuitry 42 on the lead 52 to cause the timing circuit togenerate a signal to reset the pulse height analyzer 36 in each analogcomputer 26A, 26B. The intensification control is a front paneladjustment.

The X and Y coordinate signals in the display register 84 are suppliedto a digital-to-analog converter 90 which reconverts them into X and Yanalog signals. Because the signals supplied to the converter 90 are indigital form, they will, if displayed on an oscilloscope, cause the beamof the oscilloscope to assume certain definite discrete positions. Thiswill present a dot-lil e pattern on the screen of the oscilloscope thatmay well be objectionable to a viewer. For this reason, that pattern iseliminated by providing a smoothing generator 92 that causes the dots totend to flow together and present a much more continuous pattern than isotherwise possible. The smoothing generator 92 is shown and described inreferenced patent application Ser. No. 834,478, filed June 18, 1969.

The X and Y analog signals are provided from the converter 90 throughappropriate gating means (not shown) to a rotator 94. Signals from thedifferential amplifiers 58X, 58Y may also be supplied on the leads 62X,62Y through similar gating means to the rotator. It is, of course,imperative the signals be supplied only from the converter 90 or fromthe differential amplifier 58 at any one time and that signals not besupplied simultaneously from both.

The rotator 94 is controlled by a front panel adjustment on the console,and mixes the X and Y signals in sine/cosine weights to rotate the imagebeing displayed in accordance with the viewers preference. The rotator.94 may comprise a resistor matrix for enabling the rotation of theimage on the oscilloscope 13 by fixed predetermined increments. Thisinvolves the use of a selector switch (front panel) to select aparticular resistor combination. The selection of the resistor valuesfor such a matrix is based on a formula that relates the output of thematrix into a fixed input impedance and a desired rotation of the axisabout its origin. This formula, which includes sine and cosine terms, isas follows:

X0111: in COS b in sin Q; and

our in sin 4 in C05 4 The resistors supply the values for thesine/cosine functions.

Alternatively, the rotator 94 may comprise a sine/cosine resolver, whichwill provide continuous rotation of the image by any desired amountrather than by fixed increments. In either case, the output of therotator 94 will comprise four signals rather than two. Those foursignals represent X+, X-, Y+ and Y coordinates of a scintillation.

The four signals from the rotator 94 are supplied to a pair ofdifferential amplifiers 96, which again convert them to two signalsrepresenting the X and Y coordinates of location of the scintillationoccurring in the scintillator. The output signals of the differentialamplifiers 96 are supplied to a multiplexer 98 and to a dual displaycontrol 100.

The multiplexer 98 also receives signals from the de coding matrixsection 24f through the test switch 28 on the lead 30. The multiplexer98 is essentially a switching circuit which selects the appropriatesignal to be sent to the data processor depending on the mode ofoperation selected by the operator. It, of course, depends on thesetting of the front panel control that determines. the mode ofoperation desired.

Normally, the dual display control 100 has no effect on the operation ofthe apparatus and the signals from the differential amplifiers 96 merelypass through it for display on the oscilloscope 13. However, when afront panel selector switch (not shown) is set to indicate a dualisotopetype of operation, the dual display control comes into operation. Inthat case, the control 100 serves to attenuate the Y signal by a factorof two. The X signal is also attenuated by a factor of two and shiftedto the right or to the left depending on the presence of a flag providedto the control from the display register 84 on a lead 102. If a flag ispresent, which indicates that the signal is due to. isotope A, the Xsignal is shifted to the left. If a flag is not present, which indicatesthat the signal is due to isotope B, the signal is shifted to the right,or vice versa depending on the design of the equipment.

FIGS. 3(a) and 3(b) illustrate the attenuator 22 and the decodingmatrices 24. As shown in FIG. 3(b), 19 input lines labeled P1 P19 areprovided from the 19 phototubes shown in FIG. 5. Each of these inputleads of the potentiometer, the signals provided to. all six of thedecoding matrices 24 are varied by the same amount.

Signals from all of the attenuators are provided 1 to the Z signaldecoding matrix 24a. Each signal is supplied through a variable resistor1 14 and a fixed resistor 1 16 to a summing amplifier 1 18. The variableresistors l 14 provide calibration means for each phototube output sofar as the Z signal is concerned.

Signals from the attenuators 110 corresponding to those received fromphototubes lying on the X+ side of the Y axis are provided to the matrix24b. As shown, these include signals which are provided from thephototubes P13, P15, P1, P14, P5, P2 and P3. These signals arerespectively supplied through variable resistors 1l4b and fixedresistors 11Gb to a summing amplifier 118b. The values of the resistors11612 are weighted in accordance with the distance of the particularphototube involved from the Y axis. For example, if the phototube P3 istwice as far from the Y axis as the phototube P14, the resistor 1145breceiving the signal from the phototube P3 would have one-half the valueof the resistor receiving the signal from the phototube P14. Thevariable resistors 1141) provide individual calibration for thephototubes enumerated.

Similarly, signals from the phototubes P9, PM), P8, P11, P17, P7, P18and P16 are supplied through variable resistors 1140 and fixed resistors116C to the input of a summing amplifier 1118c. The output of thesumming amplifier 1180 represents the X signal. The resistors 1160 areweighted in accordance with the location of their correspondingphototube in the same manner as the resistors 1161a.

In a similar manner, signals from the phototubes P1 1, P12, P1, P10,P18, P13 and P2 are provided through variable resistors 114d and fixedresistors 116d to a summing amplifier 118d. The output of the amplifier118d represents the Y+ output signal. Y output signals are provided fromthe matrix 242 in a similar manner through variable resistors 114:: andfixed resistors 1162. Those signals are, of course, provided from thephototubes P8, P16, P15, P4, P7, P6 and P5. Needless to say, theresistors 116d, 1l6e are weighted in the same manner as those previouslymentioned, but in accordance with the distance of the correspondingphototubes from the X axis.

Signals from the attenuators 110 are also provided through fixedresistors 120 to 19 contacts of the selector switch 122. The selectorswitch has a movable arm 112a that can connect any one of the 19contacts to the input of an amplifier 124. The output of the amplifer124 is provided through the test switch 28 to the multiplexer 98, bothof which are shown in FIG. 2. Thus, by virtue of the attenuators 110 andthe individual calibration controls 116, the outputs of all of thephototubes P1 P19 and their preamplifiers can be adjusted to provide forvariations in gain of any of the phototubes or preamplifiers.

The data processor 15 shown in FIG. 2(1)) may be any one of variousmakes or types. However, it has been found in practice that a processorknown as the Spectron 100, which is available from Picker Corporation,White Plains, New York, is preferable in this particular application. Itembodies an oscilloscope on which the various desired histograms aredisplayed, and which also serves as a calibration indicator whencalibrating the phototubes. Reference is made to the instruction manualsof that equipment for further details.

In the tape playback mode of operation, only the recorder 78 and aplayback amplifier 130 are utilized, along with the succeeding circuitryshown in FIG. 2(b). The playback amplifier 130 provides a signal to thegate 80 and to the ring counter 72 to indicate that the equipment is ina playback mode of operation. The recorded signals are supplied to theshift register 70. The functions of those portions of the equipment areshown and described in the referenced application Ser. No. 836,915,filed June 26, 1969. The remainder of the circuitry functions asdescribed in the description of normal mode of operation.

In the fast analog mode of operation, the entireanalog-to-digital-to-analog portions of the apparatus are not utilized.This includes the converters 60, the gates 62, the oscilloscope 64, thetransfer gate 50, the ring control 72, the gate 80, the shift register70, the record and playback amplifier '76 and 130, the delay 85, theflip-flop 86, the display register 84, the digital-toanalog converter 94and the smoothing generator 92. In the fast analog mode of operation,signals representing X and Y coordinates are transferred directly fromthe differential amplifiers 58X and 58Y to the rotator 94 on the leads62X, 62Y and are provided from the rotator through the multiplexer 98 tothe data proces sor 15 and to the oscilloscope 13 through the dualdisplay control 100.

We claim:

1. A display apparatus for use in a camera for producing a displayrepresentative of the spatial distribution of incident stimuli from asubject under investigation, the camera including a light-emittingelement for emitting flashes of light in response to such incidentstimuli and a plurality of light-responsive components, each of whichemits analog electrical signals in response to light flashes incidentupon it with such analog electrical signals each having an amplitudewhich is a function of the position of the light flash responded to,said display apparatus comprising:

a. an analog-to-digital converter for converting said analog electricalsignals to digital signals indicative of positions of said flashes oflight in said lightemitting element,

b. recording means for receiving and recording said digital signals;

c. playback means for playing back the recorded digital signals;

d. a digital-to-analog converter connected to said playback means forreceiving and converting said digital signals into second analogsignals, and,

e. display apparatus for providing a visual display of said radiationstimuli represented by said second analog signals in positions thatcorrespond to locations of said stimuli in said subject to provide animage of the stimuli from said subject.

2. The apparatus of claim 1, further including a smoothing generatorconnected to said digital-toanalog converter means for modifying saidsecond analog signals to present a continuous visual display on saiddisplay means.

3. The apparatus of claim 1, further including an angular displacementadjustment ciricuit interposed between said digital-to-analog converterand said display apparatus for adjustably angularly displacing saidimage on said display apparatus by a predetermined angular displacementabout a predetermined axis in order to render the image more easilyviewed.

4. in a scintillation camera for producing a visual displayrepresentative of the spatial distribution of incident radiation stimuliof at least two different energy levels from a subject underinvestigation, said camera including a light emitting mechanism capableof emitting flashes of light locatable over a two dimensional region inresponse to such incident stimuli while said light emitting mechanism isstationary with respect to the subject, said flashes having brightnesswhich is a function of the intensity of the energy levels of saidradiation stimuli in response to which such flashes are generated, and aplurality of light responsive components for emitting groups of analogelectrical signals in respone to said flashes, each of said signalgroups having a combined amplitude which is a function of the brightnessof the flash in response to which said signal group is generated, saidsignal groups each bearing analog information describing the location ofthe flash in response to which said signal group is emitted, theimprovement comprising:

a. at least two discriminating circuits each connected to sense thecombined amplitude of each of said analog electrical signal groups, eachof aid discriminating circuits being responsive to only those groups ofanalog electrical signals having a combined amplitude in a differentpredetermined range to produce an actuation signal;

b. an indicator circuit responsive to said actuation by one of saiddiscriminating circuits to provide an indication associated with each ofsaid analog signal groups to which said one discriminating circuit isresponsive; and

c. a display apparatus connected to receive and maintain said signalgroups and being responsive to said analog signal groups and saidindication for providing a separate visual representation of the spatiallocation of said radiation stimuli in response to which said analogsignal groups having an indication associated therewith are generatedand a separate visual representation of the spatial location of saidradiation stimuli in response to which said analog signal groups havingno indication associated therewith are generated.

5, The improvement of claim 4, wherein each of said discriminatingcircuits comprises a pulse height analyzer to enable the selectiveresponse of said discriminating circuit to only those analog signalgroups having a combined amplitude lying within said predeterminedrange.

6. The improvement of claim 4, wherein said indica' tor circuitcomprises:

a flag signal generator connected to one of said discriminating circuitsfor providing a flag signal associated with only those analog signalsgroups to which said one of said discriminating circuits is responsiveto indicate the amplitude range in which said associated analog signalgroups lie. 7. The improvement of claim 4, wherein said displayapparatus, comprises:

a. two portions, and b. means for separating the analog signal groups towhich each of said discriminating circuits is respectively responsivefor displaying said visual repre-' sentations of the stimulicorresponding to said separated analog signal groups on different onesof said portions of said display apparatus.

8. The improvement of claim 6, wherein said display apparatus isresponsive to one of the presence and absence of said flag signalassociated with each said analog signal group to control said visualrepresentation of said energy level of said stimulus in response towhich said analog signal group is generated.

9. The improvement of claim 4, further comprising a. a digital to analogconverter connected to said ana- I log to digital converter for'reconverting said digital signals to analog form; and

b. a display device connected to said digital to analog converter todisplay a visual representation of said reconverted digital signals.

13. The improvement of claim 12, further comprising: V

angular displacement circuitry connected to said display screen forrotating the visual representation on the screen by a predeterminedamount to assist in viewing the display.

14. The improvement of claim 4, further comprising:

a gating circuit connected between said discriminating circuits toprevent the simultaneous operation of more than one of saiddiscriminating circuits.

15. The improvement of claim 4, further including a calibration systemfor said light responsive components comprising:

a. a selector circuit for sampling the output of each of a plurality ofsaid light-responsive components and V b. an attenuator circuit havingan output and means for varying at its said output the level of theoutput from each of said plurality of said light responsive component.

16. A dual-isotope imaging scintillation camera for producing a visualdisplay representative of the spatial distribution of incident radiationstimuli of at least two different energy ranges emanating from a subjectunder investigation, said camera comprising:

a. a light emitting mechanism for emitting flashes of light locatableover a two dimensional region in response to the occurrence of saidincident stimuli while said light emitting mechanism is stationary withrespect to the subject, said flashes having a brightness which is afunction of the intensity of the energy level of said radiation stimuliin response to which such flashes are generated, a plurality of lightresponsive components optically coupled to said light emitting mechanismfor emitting groups of analog electrical signals in response to saidflashes, each of said signal groups having a combined amplitude which isa function of the brightness of the flash in response to which saidsignal group is generated, and said signal groups each bearing analoginformation describing the location over said two-dimensional region ofthe flash in response to which said signal group is emitted,

c. at least two discriminating circuits each connected to sense thecombined amplitude of each of said analog electrical signal groups, oneof said discriminating circuits being responsive to only those groups ofanalog electrical signals having a combined amplitude in apredeterminedrange to generate an actuation signal,

(1. an indicator circuit responsive to said actuation signal by one ofsaid discriminating circuitislto provide an indication associated witheach of said analog signal groups to which said one discriminatingcircuit is responsive, and

e. a display apparatus connected to said control circuit output andbeing responsive to said analog signal groups and said indication forproviding a separate visual representation of the spatial location ofsaid radiation stimuli in response to which said analog signal groupshaving an indication associated therewith are generated and a secondseparate visual representation of the spatial location of said radiationstimuli in response to which said analog signals having no indicationassociated therewith are generated.

17. The scintillation camera of claim 16, wherein each of saiddiscriminating circuits comprises a pulse 0 height analyzer to enablethe selective response of said to which said at least one of saiddiscriminating circuits is responsive to indicate the amplitude range inwhich said associated analog signal groups lie.

19. The scintillation camera of claim 16, wherein said display apparatuscomprises two portions, and means for separating the analog signalgroups to which each of said discriminating circuits is respectivelyresponsive for displaying said visual representations of the stimulicorresponding to said separated analog signal groups corresponding tothe respective ones of said discriminating circuits on different ones ofsaid portions of said display apparatus.

20. The scintillation camera of claim 16, wherein said display apparatusis responsive to said flag signal to separately display a representationof the stimuli represented by those signal groups having said flagsignal associated therewith and a representation of the stimulirepresented by those signal groups not having said flag signalassociated therewith.

21. The scintillation camera of claim 16, further comprising:

an analog to digital converter interposed between said discriminatingcircuit and said display apparatus for converting said signal groups todigital signals.

22. The scintillation camera of claim 21, wherein;

said analog to digital converter is a height to time converter.

23. The scintillation camera of claim 21, wherein said display apparatuscomprises:

a. a shift register connected to store said converted digital signals;and

b. digital display means connected to said shift register to providevisual display representative of said digital signals.

24. The scintillation camera of claim 21, wherein said display apparatuscomprises:

a. a digital to analog converter connected to said analog to digitalconverter; and

b. a display screen connected to said digital to analog converter todisplay representation of said reconverted digital signals.

25. The scintillation camera of claim 24, further comprising: angulardisplacement circuitry connected to said display screen for rotating thevisual representation on the screen by a predetermined amount to assistin viewing the display.

26. The scintillation camera of claim 16, further comprising:

a gating circuit connected between said discriminating circuits toprevent the simultaneous operation by more than one of saiddiscriminating circuits.

27. The camera of claim 16, further including a calibration system forsaid light responsive components comprising:

a. a selector circuit for sampling the output of at least one of saidlight-responsive components, and

b. an attenuator having an output and connected to said light responsivecomponents for varying at its said output the level of the output fromsaid light responsive component.

28. A method for producing a visual display representative of thespatial distribution of incident radiation stimuli of at least twodifferent energy ranges emanating from a subject under investigation,said method including the steps of:

a. generating signals in response to the occurrence of said radiationstimuli, each of said signals having a combined amplitude which is afunction of the level of radiation of the radiation stimulus in responseto which said signal is generated and said signals each bearinginformation describing the location of the radiation stimulus inresponse to which said each signal group is generated,

b. sensing the combined amplitude of each of said signals,

0. generating an indication associated with only those of said signalshaving a combined amplitude lying within a predetermined range, and.

d. maintaining said signals and generating in response to said signalsand said indication a separate pattern of signals representing a visualrepresentation of the spatial location of the radiation stimuli inresponse to which said signals having an indication associated therewithare generated, and generating a second pattern of signals representing aseparate visual representation of the spatial location of the radiationstimuli in response to which said signals having no indicationassociated therewith are generated.

29. The method of claim 28, wherein the step of generating an indicationcomprises generating a flag signal to indicate the combined amplituderange of said signals with which such flag signal is associated.

30. The method of claim 28, wherein said signals are analog in form,said method further comprising the step of:

converting said signals from analog to digital form before generatingsaid visual display thereof.

31. The method of claim 30 further comprising the step of:

reconverting said digital converted signals to analog form, anddisplaying said rcconverted analog signals on a display screen.

32. The method of claim 31 further comprising angularly displacing thevisual representation of said reconverted analog signals by apredetermined amount about a predetermined axis in order to assist inrendering the display more easily viewable.

33. A discriminator for an apparatus for producing a visual displayrepresentative of the spatial distribution of incident radiation stimuliof at least two different energy ranges emanating from a subject underinvestigation, said discriminator comprising:

a. A signal generator for producing signals in response to saidradiation stimuli, each of said signals having an amplitude which is afunction of the radiation level of the stimulus in response to whichsaid signal is generated, said signals each further bearing informationdescribing the location of the radiation stimulus in response to whichsaid signal is generated;

b. an indication generator connected to receive said signals to sensethe amplitude of each of said signals and to provide an indicator signalassociated with each of said signals the amplitude of which lies withina predetermined range, and

c. a display apparatus connected to receive said sig nals and saidindicator signal and being responsive to said signals and said indicatorsignal for providing a visual representation of the spatial location ofsaid radiation stimuli in response to which said signals having anindicator signal associated therewith are generated and a second visualrepresentation of the spatial location of said radiation stimuli inresponse to which said signals having no indicator signal associatedtherewith are generated. 34. The discriminator of claim 33, wherein saidindication generator comprises a pulse height analyzer for sensingwhether the amplitudes of said signals lies within said predeterminedrange. a

35. The discriminator of claim 33, wherein said indication generator isa flag signal generator for generat ing flag signals to indicate theamplitude range in which said associated signals lie.

36. The discriminator of claim 33, further comprising a first converterconnected to receive said signals ,to convert said signals to digitalform prior to the display

1. A DISPLAY APPARATUS FOR USE IN A CAMERA FOR PRODUCING A DISPLAY REPRESENTATIVE OF THE SPATIAL DISTRIBUTION OF INCIDENT STIMULI FROM A SUBJECT UNDER INVESTIGATION, THE CAMERA INCLUDING A LIGHT-EMITING ELEMENT FOR EMITING FLASHES OF LIGHT IN RESPONSE TO SUCH INCIDENT STIMULI AND A PLURALITY OF LIGHTRESPONSIVE COMPONENTS, EACH OF WHICH EMITS ANALOG ELECTRICAL SIGNALS IN RESPONSE TO LIGHT FLASHES INCIDENT UPON IT WITH SUCH ANALLG ELECTRICAL SIGNALS EACH HAVING AN AMPLITUDE WHICH IS A FUNCTION OF THE POSITION OF THE LIGHT FLASH RESPONDED TO, SAID DISPLAY APPARATUS COMPRISING: A. AN ANALOG-TO-DIGITAL CONVERTER FOR CONVERTING SAID ANALOG ELECTRICAL SIGNALS TO DIGITAL SIGNALS INDICATIVE OF POSITIONS OF SAID FLASHES OF LIGHT IN SAID LIGHT-EMITING ELEMENT, B. RECORDING MEANS FOR RECEIVING AND RECORDING SAID DIGITAL SIGNALS, C. PLAYBACK MEANS FOR PLAYING BACK THE RECORDED DIGITAL DIGNALS, D. S DIGITAL-TO-ANALOG CONVERTER CONNECTED TO SAID PLAYBACK MEANS FOR RECEIVING AND CONVERTNG SAID DIGITAL SIGNALS INTO SECOND ANALOG SIGNALS, AND, E. DISPLAY APPARATUS FOR PROVIDING A VISUAL DISPLAY OF SAID RADIATION STIMULI REPRESENTED BY SAID SECOND ANALOG SIGNALS IN POSITIONS THAT CORRESPOND TO LOCATIONS OF SAID STIMULI IN SAID SUBJECT TO PROVIDE AN IMAGE OF THE STIMULI FROM SAID SUBJECT.
 2. The apparatus of claim 1, further including a smoothing generator connected to said digital-to-analog converter means for modifying said second analog signals to present a continuous visual display on said display means.
 3. The apparatus of claim 1, further including an angular displacement adjustment ciricuit interposed between said digital-to-analog converter and said display apparatus for adjustably angularly displacing said image on said display apparatus by a predetermined angular displacement about a predetermined axis in order to render the image more easily viewed.
 4. In a scintillation camera for producing a visual display representative of the spatial distribution of incident radiation stimuli of at least two different energy levels from a subject under investigation, said camera including a light emitting mechanism capable of emitting flashes of light locatable over a two dimensional region in response to such incident stimuli while said light emitting mechanism is stationary with respect to the subject, said flashes having brightness which is a function of the intensity of the energy levels of said radiation stimuli in response to which such flashes are generated, and a plurality of light responsive components for emitting groups of analog electrical signals in respone to said flashes, each of said signal groups having a combined amplitude which is a function of the brightness of the flash in response to which said signal group is generated, said signal groups each bearing analog information describing the location of the flash in response to which said signal group is emitted, the improvement comprising: a. at least two discriminating circuits each connected to sense the combined amplitude of each of said analog electrical signal groupS, each of aid discriminating circuits being responsive to only those groups of analog electrical signals having a combined amplitude in a different predetermined range to produce an actuation signal; b. an indicator circuit responsive to said actuation by one of said discriminating circuits to provide an indication associated with each of said analog signal groups to which said one discriminating circuit is responsive; and c. a display apparatus connected to receive and maintain said signal groups and being responsive to said analog signal groups and said indication for providing a separate visual representation of the spatial location of said radiation stimuli in response to which said analog signal groups having an indication associated therewith are generated and a separate visual representation of the spatial location of said radiation stimuli in response to which said analog signal groups having no indication associated therewith are generated.
 5. The improvement of claim 4, wherein each of said discriminating circuits comprises a pulse height analyzer to enable the selective response of said discriminating circuit to only those analog signal groups having a combined amplitude lying within said predetermined range.
 6. The improvement of claim 4, wherein said indicator circuit comprises: a flag signal generator connected to one of said discriminating circuits for providing a flag signal associated with only those analog signals groups to which said one of said discriminating circuits is responsive to indicate the amplitude range in which said associated analog signal groups lie.
 7. The improvement of claim 4, wherein said display apparatus comprises: a. two portions, and b. means for separating the analog signal groups to which each of said discriminating circuits is respectively responsive for displaying said visual representations of the stimuli corresponding to said separated analog signal groups on different ones of said portions of said display apparatus.
 8. The improvement of claim 6, wherein said display apparatus is responsive to one of the presence and absence of said flag signal associated with each said analog signal group to control said visual representation of said energy level of said stimulus in response to which said analog signal group is generated.
 9. The improvement of claim 4, further comprising: an analog to digital converter interposed between said discriminator circuits and said display apparatus for converting said analog signal groups to digital signals.
 10. The improvement of claim 9, wherein: said analog to digital converter includes a height to time converter.
 11. The improvement of claim 9, wherein said display apparatus comprises: a. a shift register connected to store said converted digital signals; and b. digital display means connected to said shift register to provide a visual display representative of said digital signals.
 12. The improvement of claim 9, wherein said display apparatus comprises: a. a digital to analog converter connected to said analog to digital converter for reconverting said digital signals to analog form; and b. a display device connected to said digital to analog converter to display a visual representation of said reconverted digital signals.
 13. The improvement of claim 12, further comprising: angular displacement circuitry connected to said display screen for rotating the visual representation on the screen by a predetermined amount to assist in viewing the display.
 14. The improvement of claim 4, further comprising: a gating circuit connected between said discriminating circuits to prevent the simultaneous operation of more than one of said discriminating circuits.
 15. The improvement of claim 4, further including a calibration system for said light responsive components comprising: a. a selector circuit for sampling the output of each of a plurality of said light-responsive components and b. an attenuaTor circuit having an output and means for varying at its said output the level of the output from each of said plurality of said light responsive component.
 16. A dual-isotope imaging scintillation camera for producing a visual display representative of the spatial distribution of incident radiation stimuli of at least two different energy ranges emanating from a subject under investigation, said camera comprising: a. a light emitting mechanism for emitting flashes of light locatable over a two dimensional region in response to the occurrence of said incident stimuli while said light emitting mechanism is stationary with respect to the subject, said flashes having a brightness which is a function of the intensity of the energy level of said radiation stimuli in response to which such flashes are generated, b. a plurality of light responsive components optically coupled to said light emitting mechanism for emitting groups of analog electrical signals in response to said flashes, each of said signal groups having a combined amplitude which is a function of the brightness of the flash in response to which said signal group is generated, and said signal groups each bearing analog information describing the location over said two-dimensional region of the flash in response to which said signal group is emitted, c. at least two discriminating circuits each connected to sense the combined amplitude of each of said analog electrical signal groups, one of said discriminating circuits being responsive to only those groups of analog electrical signals having a combined amplitude in a predetermined range to generate an actuation signal, d. an indicator circuit responsive to said actuation signal by one of said discriminating circuitis to provide an indication associated with each of said analog signal groups to which said one discriminating circuit is responsive, and e. a display apparatus connected to said control circuit output and being responsive to said analog signal groups and said indication for providing a separate visual representation of the spatial location of said radiation stimuli in response to which said analog signal groups having an indication associated therewith are generated and a second separate visual representation of the spatial location of said radiation stimuli in response to which said analog signals having no indication associated therewith are generated.
 17. The scintillation camera of claim 16, wherein each of said discriminating circuits comprises a pulse height analyzer to enable the selective response of said discriminating circuit to only those analog signal groups having a combined amplitude lying within said predetermined range.
 18. The scintillation camera of claim 16, wherein said indicator circuit comprises: a flag signal generator connected to at least one of said discriminating circuits for providing a flag signal associated with only those analog signal groups to which said at least one of said discriminating circuits is responsive to indicate the amplitude range in which said associated analog signal groups lie.
 19. The scintillation camera of claim 16, wherein said display apparatus comprises two portions, and means for separating the analog signal groups to which each of said discriminating circuits is respectively responsive for displaying said visual representations of the stimuli corresponding to said separated analog signal groups corresponding to the respective ones of said discriminating circuits on different ones of said portions of said display apparatus.
 20. The scintillation camera of claim 16, wherein said display apparatus is responsive to said flag signal to separately display a representation of the stimuli represented by those signal groups having said flag signal associated therewith and a representation of the stimuli represented by those signal groups not having said flag signal associated therewith.
 21. The scintillation camera of claim 16, further comprising: an analog To digital converter interposed between said discriminating circuit and said display apparatus for converting said signal groups to digital signals.
 22. The scintillation camera of claim 21, wherein; said analog to digital converter is a height to time converter.
 23. The scintillation camera of claim 21, wherein said display apparatus comprises: a. a shift register connected to store said converted digital signals; and b. digital display means connected to said shift register to provide visual display representative of said digital signals.
 24. The scintillation camera of claim 21, wherein said display apparatus comprises: a. a digital to analog converter connected to said analog to digital converter; and b. a display screen connected to said digital to analog converter to display representation of said reconverted digital signals.
 25. The scintillation camera of claim 24, further comprising: angular displacement circuitry connected to said display screen for rotating the visual representation on the screen by a predetermined amount to assist in viewing the display.
 26. The scintillation camera of claim 16, further comprising: a gating circuit connected between said discriminating circuits to prevent the simultaneous operation by more than one of said discriminating circuits.
 27. The camera of claim 16, further including a calibration system for said light responsive components comprising: a. a selector circuit for sampling the output of at least one of said light-responsive components, and b. an attenuator having an output and connected to said light responsive components for varying at its said output the level of the output from said light responsive component.
 28. A method for producing a visual display representative of the spatial distribution of incident radiation stimuli of at least two different energy ranges emanating from a subject under investigation, said method including the steps of: a. generating signals in response to the occurrence of said radiation stimuli, each of said signals having a combined amplitude which is a function of the level of radiation of the radiation stimulus in response to which said signal is generated and said signals each bearing information describing the location of the radiation stimulus in response to which said each signal group is generated, b. sensing the combined amplitude of each of said signals, c. generating an indication associated with only those of said signals having a combined amplitude lying within a predetermined range, and d. maintaining said signals and generating in response to said signals and said indication a separate pattern of signals representing a visual representation of the spatial location of the radiation stimuli in response to which said signals having an indication associated therewith are generated, and generating a second pattern of signals representing a separate visual representation of the spatial location of the radiation stimuli in response to which said signals having no indication associated therewith are generated.
 29. The method of claim 28, wherein the step of generating an indication comprises generating a flag signal to indicate the combined amplitude range of said signals with which such flag signal is associated.
 30. The method of claim 28, wherein said signals are analog in form, said method further comprising the step of: converting said signals from analog to digital form before generating said visual display thereof.
 31. The method of claim 30 further comprising the step of: reconverting said digital converted signals to analog form, and displaying said reconverted analog signals on a display screen.
 32. The method of claim 31 further comprising angularly displacing the visual representation of said reconverted analog signals by a predetermined amount about a predetermined axis in order to assist in rendering the display more easily viewable.
 33. A discriminator for an apparatus for producing a visual display representative of the spatial distribution of incident radiation stimuli of at least two different energy ranges emanating from a subject under investigation, said discriminator comprising: a. A signal generator for producing signals in response to said radiation stimuli, each of said signals having an amplitude which is a function of the radiation level of the stimulus in response to which said signal is generated, said signals each further bearing information describing the location of the radiation stimulus in response to which said signal is generated; b. an indication generator connected to receive said signals to sense the amplitude of each of said signals and to provide an indicator signal associated with each of said signals the amplitude of which lies within a predetermined range, and c. a display apparatus connected to receive said signals and said indicator signal and being responsive to said signals and said indicator signal for providing a visual representation of the spatial location of said radiation stimuli in response to which said signals having an indicator signal associated therewith are generated and a second visual representation of the spatial location of said radiation stimuli in response to which said signals having no indicator signal associated therewith are generated.
 34. The discriminator of claim 33, wherein said indication generator comprises a pulse height analyzer for sensing whether the amplitudes of said signals lies within said predetermined range.
 35. The discriminator of claim 33, wherein said indication generator is a flag signal generator for generating flag signals to indicate the amplitude range in which said associated signals lie.
 36. The discriminator of claim 33, further comprising a first converter connected to receive said signals to convert said signals to digital form prior to the display of said visual representations of said signals.
 37. The discriminator of claim 36, wherein said display apparatus further comprises: a. a digital to analog converter connected to said first converter, to reconvert said digital signals to analog form, and b. a display screen connected to said digital to analog converter to display a visual representation of said reconverted analog signals.
 38. The discriminator of claim 37, further comprising: angular displacement circuitry conducted to said display screen for rotating the visual representation on the screen by a predetermined amount about a predetermined axis. 